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First record of a middle Cenomanian caprinuloideid rudist (Hippuritida, Bivalvia) from Montana, USA, and its geographical and stratigraphical significance
Cretaceous Research 46 (2013) 59e64
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First record of a middle Cenomanian caprinuloideid rudist (Hippuritida, Bivalvia) from Montana, USA, and its geographical and stratigraphical significance Simon F. Mitchell Department of Geography and Geology, The University of the West Indies, Mona, Kingston 7, Jamaica
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 June 2013 Accepted in revised form 3 September 2013 Available online 23 October 2013
The new caprinoidean rudist bivalve Cobbanicaprina bighornensis gen. nov., sp. nov. is described from the upper middle Cenomanian of Big Horn County, Montana, USA. Cobbanicaprina gen. nov. is closely related to Mexicaprina and differs from that form in the absence of an external ligamental groove. The presence of Cobbanicaprina gen. nov. in the middle Cenomanian indicates that the Caprinuloideidae did not become extinct at the top of the Albian and persisted into the Cenomanian. The presence of this specimen so far north in the Western Interior Seaway is attributed to a dried-out individual specimen having been transported post-mortem by currents. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Caprinoidea Caprinuloideidae Cenomanian Rudist bivalve Montana
1. Introduction The caprinoids (rudist bivalves) dominated the carbonate platforms of the mid Cretaceous but show contrasting patterns of development in the Old World and New World. In the Old World, the Caprinidae appeared in the Hauterivian and evolved to a peak of diversity in the early Aptian (Kauffman and Johnson, 1988; Skelton and Masse, 1998; Steuber and Löser, 2000). Following a mid Aptian extinction associated with Oceanic Anoxic Event 1a (OAE1a: Selli event), diversity remained low during the Albian, with a second peak in diversity during the Cenomanian before the group became extinct at OAE2 (Bonarelli event) in the late Cenomanian (Kauffman and Johnson, 1988; Philip and Airaud-Crumiere, 1991; Steuber and Löser, 2000). In contrast, the Caprinuloideidae of the New Word, which also appeared in the Hauterivian and saw a mid-early Aptian diversity peak and a mid Aptian extinction, reached their peak of diversity during the Albian and disappeared near the top of that stage, possibly at OAE1d (Breistroffer event) (Kauffman and Johnson, 1988; Skelton and Masse, 1998; Steuber, 2002; Scott, 2002; Scott and Hinote, 2007; Mitchell, 2013). Rudist bivalves characterized carbonate platform margins with less diverse assemblages in platform interior facies (Scott, 1990) and were particularly susceptible to Oceanic Anoxic Events (Schlanger and Jenkyns, 1976), when oxygen depleted waters E-mail address: [email protected]. 0195-6671/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cretres.2013.09.001
invaded the platforms and poisoned the biota leading to mass extinctions. Rudist bivalves are also occasionally found away from platform limestone facies in diverse sedimentary rock types ranging from chalks to mudstones to sandstones. In many cases their highly porous shells, which were filled with cells or pallial canals, may have enabled specimens that had dried out on beaches to float considerably distances (just as pumice can) and eventually when their shells became waterlogged they would sink to the sea floor. Away from the carbonate platforms of the AptianeAlbian of Texas and Arizona (Scott, 1981; Scott, 1990), rudist bivalves are rare in North American deposits (Anderson, 1958; Cobban et al., 1991; Hook and Cobban, 2013; Schumacher, 2013) and rather than specimens growing in situ might be the result of such floating specimens. Amongst these occurrences, specimens containing pallial canals have often been referred to Tchthyosarcolithes or Tchthyosarcolithes corelloidea (Hall and Meek). The revision of some of these records, as well as new records, indicates some of these specimens recorded from the Albian belong to the Caprinuloideidae (Iba et al., 2009; Sano et al., 2013). To date, however, no undoubted caprinuloideids have been recorded from undoubted post-Albian strata. During a visit to the Smithsonian in 2012, I discovered in the collections a well-preserved specimen of a pallial-canal bearing rudist from the upper middle Cenomanian of Montana (Fig. 1). This specimen has very good documentation and forms the basis of the current paper.
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Fig. 1. Map of North America showing the Western Interior Seaway extending from Texas to Canada and the location of reported specimens of Cenomanian (solid circles) and Turonian (open circles) rudists (data from Cobban et al., 1991; Hook and Cobban, 2013; Schumacher, 2013). Collection location of Cobbanicaprina bighornensis gen. nov., sp. nov. is the large black circle in Montana. Abbreviations for US states: MT, Montana; ND, North Dakota; SD, South Dakota; CO, Colorado; NE, Nebraska; AZ, Arizona; NM, New Mexico; TX, Texas; OK, Oklahoma. Land areas (Laramidia and Appalachia) shaded.
2. Provenance of specimen The specimen (USNM 547507) was collected from USGS Locality number 22869, and has the details of the specimen written on what is clearly an old piece of paper with the specimen that reads “Tchthyosarcolithes corelloidea {sic} from base of Soap Creek Bentonite at the top of Frontier Formation, Loc. NW ¼, SW ¼ Sec 31, T 7 S, R 32 E, Big Horn County, Mont.” (Fig. 2), which is in the Hardin District, and the specimen is listed as having been collected by “S.H. Patterson Sept. 1947” (Fig. 2). The specimen was presumably collected during Knechtel and Patterson’s study of the bentonites of Montana and Wyoming (Knechtel and Patterson, 1952, 1955, 1956, 1962). Sam H. Patterson joined the study in 1947 and measured and sampled the bentonite beds in the late summer and autumn of 1947 (Knechtel and Patterson, 1956, p. 1, 4) which is consistent with the collection date on the label (Fig. 2). Silicification of the specimen is
Fig. 2. Specimen label for Cobbanicaprina bighornensis gen. nov., sp. nov. preserved with the specimen in the Smithsonian.
also consistent with silicification associated with bentonites in Montana (Knechtel and Patterson, 1956, p. 40) as well as with some silicified specimens of the ammonite Cunningtoniceras amphibolum fallense Cobban lying on top of the Soap Creek Bentonite (Cobban, 1987, p. 15). Additionally, the Soap Creek Bentonite is referred to as lying on top of the Frontier Formation, which would have been consistent with earlier literature (e.g., Richards and Rogers, 1951), but which was changed by Knechtel and Patterson (1956) who placed the Soap Creek Bentonite in the Hardin district in the upper part of the Belle Fourche Member of the Cody Shale. The consistency of the information on a clearly old, and probably original label, identifying the specimen as a Tchthyosarcolithes (a canal bearing rudist) and the correct links to the time when Sam H. Patterson was doing fieldwork, demonstrate that the origin and the age of the specimen can be relied upon. The matrix in the body cavity has, however, been silicified preventing a direct comparison with the sediments of the Frontier Formation or Belle Fourche Member or checking for nannofossils. The locality NW ¼, SW ¼ Sec 31, T 7 S, R 32 E from which the rudist was collected is situated in the Big Horn Mountains to the south of the Soap Creek oil field within the drainage area of Soap Creek, about 20 miles (32 km) south of St. Xavier (Knechtel and Patterson, 1956, p. 86). In this area the Soap Creek bentonite is extensively exposed and averages 16 feet (5 m) in thickness. The Soap Creek Bentonite (also called the F Bed, X bentonite or Greyered bentonite), dated using 40Ar/39Ar at 94.93 .53 Ma (Obradovich, 1993; Fig. 3), is a thick regional marker in the Acanthoceras amphibolum ammonite zone. Richards and Rogers (1951) stated that the Soap Creek Bentonite was situated at the top of the siliciclastic deltaic sandstones of the Frontier Formation in Big Horn and Yellowstone Counties, Montana. In contrast, Knechtel and Patterson (1956) placed the Soap Creek Bentonite in the upper part of the Belle Fourche Member of the Cody Shales (but now regarded as member in the Frontier Formation) based on the presence of marine fossils and the dominance of shale lithologies in Big Horn County. The Frontier Formation represents a series of deltas on the western margin of the Western Interior Seaway produced either through progradation or forced regression (e.g.,
Fig. 3. Stratigraphy of Cenomanian in Montana and Wyoming with ammonite zones and dated bentonites (after Gale et al., 2008). Cobbanicaprina bighornensis gen. nov. sp. nov. was collected from the Soap Creek Bentonite.
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Bhattacharya and Willis, 2001; Clark, 2010; Hutsky, 2011; Hurd, 2012). 3. Systematic Palaeontology The classification used here follows Carter et al. (2011), Skelton (2013) and Mitchell (2013). Abbreviations used: RV, right valve; LV, left valve; ct, central tooth; at/ats, anterior tooth/socket; pt/pts, posterior tooth/socket; am, anterior myophore; pm, posterior myophore. Order Hippuritida Newell, 1965 Suborder Radiolitidina Skelton, 2013 Superfamily Caprinoidea d’Orbigny, 1847 Family Caprinuloideidae Damestoy, 1971 Subfamily Caprinuloideinae Damestoy, 1971 Genus Cobbanicaprina gen. nov. Type species. Cobbanicaprina bighornensis gen. nov. sp. nov. Derivation of name. After William A. Cobban for his work on the Cretaceous deposits of North America. Diagnosis. A genus of Caprinuloideinae with an elongate cylindrical RV. There is no external ligamental groove. The socket for the at is large and bifid and that for the pt is small. The am is attached to a surface (ledge) on the anterior side of the shell; the pm fitted into an elongate socket on the posterior side of the at socket. The ct is ‘knee’-shaped. The shell wall and ct are filled with rounded to polygonal pallial canals. Distribution. Only known from the upper middle Cenomanian of Big Bend County, Montana. Discussion. Although only a single specimen is available, the specimen shows distinctive diagnostic characters that not only allows it to be described but allows its relationship with the subfamily Caprinuloideinae to be evaluated in detail. As such the erection of a new genus based on a single RV is considered warranted. Cobbanicaprina gen. nov. shows characters in common with many Albian caprinuloideids but also has differences (Fig. 4). Like Neokimbleia Mitchell and Youngicaprina Mitchell, Cobbanicaprina gen. nov. lacks an external ligamental groove. In Caprinuloidea Palmer and Youngicaprina the ct is straight and extends down to the body cavity (Fig. 4.5e4.6); in Mexicaprina Coogan and Cobbanicaprina the ct is knee-shaped extending first towards the posterior side of the shell and then bending towards the ventral margin of the shell (Fig. 4.1e4.2); in Kimbleia Coogan and Neokimbleia the ct is thickened dorso-ventrally, extends a short way towards the posterior side of the shell and then extends towards the ventral margin as a narrow septum (Fig. 4.2e4.3). The form of the pm in Cobbanicaprina (judging from the form of the cavity it fitted into in the RV) is similar to that of Mexicaprina, Kimbleia and Neokimbleia and did not extend along the posterior side of the body cavity (Fig. 4.1e 4.4). Youngicaprina is further differentiated by the form of its myophores, particularly the bladed am. Some specimens of Mexicaprina also have a bifid tooth which is also seen in Immanitas Palmer (Aguilar Pérez, 2008). Cobbanicaprina gen. nov. can therefore be seen as an evolutionary development from Mexicaprina that developed by the loss of an external ligamental groove. This is comparable to the loss of the external ligamental grooves in the evolution of Neokimbleia from Kimbleia and of Youngicaprina from Texicaprina Coogan (Mitchell, 2013). Cobbanicaprina gen. nov. differs from Tchthyosarcolithes in the form of its pm. In Tchthyosarcolithes the pm attaches directly to the body cavity, whereas in Cobbanicaprina gen. nov. it fits into an accessory cavity separated from the body cavity by a septum. Equally, Cobbanicaprina is distinguished from Old World
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Cenomanian caprinids such as Caprina by its myocardinal arrangement with the pm being rotated downwards and outwards from the LV to face outwards onto the accessory cavity wall in the RV (the converse is true in Caprina and other caprinids). Cobbanicaprina bighornensis gen. nov. sp. nov. Figs. 4.1, 5 Derivation of name. After Big Horn County, Montana, where the specimen was collected. Holotype. Smithsonian Institute, No. USNM 547507, from the base of the Soap Creek Bentonite (upper middle Cenomanian), Big Horn County, Montana. Diagnosis. Same as genus. Description. The holotype is an incomplete RV with a preserved length of 169 mm and a maximum diameter of 57 mm. The specimen has been silicified preserving full details of the shell construction. Parts of the exterior have been weathered away to show the pallial canals comprising the outer layer of the inner shell material, but around part of the exterior the very thin outer layer is preserved. The body cavity is rounded pentagonal in form (Fig. 5.1), and has a maximum diameter of 22 mm which is about 37% of the estimated original diameter of the shell at that point. The body cavity is filled with spaced concave to commissure tabulae (Fig. 5.3). The myocardinal features can be seen in a natural transverse cross section (Fig. 5.1) as well as on the upper weathered surface of the specimen (Fig. 5.2). This upper weathered surface has tabulae in the body cavity and is at a level somewhere below the commissure of the original shell. The socket for the at tooth is large and bifid, with a wedge of pallial canal-bearing shell material forming a triangular ridge on the antero dorsal side (Fig. 5.1). The socket for the pt is much smaller than that of the at, and is pear-shaped. On its dorsal side, the socket for the pt is partially penetrated by a short, narrow ridge (Fig. 5.1). There is no external ligamental groove. The socket/attachment for the am is seen as a surface within the pallial canal-bearing shell structure on the anterior side of the shell; this surface begins near the triangular ridge which projects into the at socket, and runs along the anterior side of the body cavity about midway through the shell structure. The socket for the pm is a dorso-ventrally elongated cavity on the posterior side of the at socket, and is filled with four larger polygonal pallial canals and several triangular smaller ones (Fig. 5.1). The ct is ‘knee’-shaped, the part between the sockets for the pt and at being filled with small pallial canals and the portion between the socket for the am and cavity for the pm being filled with elongated pallial canals. The pallial canals in the outermost part of the shell structure, where they are preserved, range from slightly to strongly elongated; some are weakly pyriform with their outer ends being a little narrower than their inner ends. The remainder of the shell structure is filled with rounded to polygonal pallial canals, which contain concave tabulae. 4. Discussion The discovery of a Cenomanian caprinuloideinid requires a review of the evolutionary development of the Caprinuloideidae. While caprinuloideids were widespread in the Aptian and Albian of the New World, the end of the Albian saw a major demise of carbonate platforms across the region (Kauffman and Johnson, 1988; Steuber and Löser, 2000). In North America uplift of the American Cordillera (Wyld et al., 2006) saw the influx of fine grained clastics in the latest Albian to Cenomanian caused the collapse of carbonate platforms of Arizona and Texas and the disappearance of the caprinuloideids. Further south in the Caribbean province, carbonate
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Fig. 4. Comparison of the RV of Cobbanicaprina gen.nov. with RVs of selected Albian caprinuloideids. All specimens shown in transverse section adumbonal view (cross sections where appropriate, flipped horizontally, so all specimens are viewed in same orientation) with the body cavity placed at the bottom. 1. Cobbanicaprina bighornensis gen nov. sp. nov., transverse cross section, original abumbonal view (here flipped horizontally), showing myocardinal features (USNM 547507); 2, Mexicaprina quadrata Alencáster and Oviedo-García, RV (IGM.4581), apertural face, late Albian of El Madroño, state of Querétaro, central Mexico; 3, Kimbleia albrittoni (Perkins 1960), RV (UT.203571), original abumbonal view (here flipped horizontally), transverse cross section, Segovia Formation, Lopez Ranch, Kimble County, Texas; 4, BeE, Neokimbleia planata (Conrad). RV (IGM.2575), original abumbonal view (here flipped horizontally), transverse cross section, El Abra Formation, Mexico; 5, Youngicaprina gloria Mitchell, RV (IGM.7643), apertural view showing myocardinal elements, late Albian of El Madroño, state of Querétaro, central Mexico; 6, Caprinuloidea romeri Mitchell, transverse section of RV, original abumbonal view (here flipped horizontally), showing teeth and myophores (SI.USNM.PAL.534223), Edwards Limestone, Whitney Dam, Texas. Abbreviations: l, ligament; ats, anterior tooth socket; ct, central tooth; pts, posterior tooth socket; am, anterior myophore; pm, posterior myophore; bc, body cavit. Scale bars, 20 mm.
platforms had been widespread in the Greater Antilles and northern South America (e.g., Rojas et al., 1996; Brown and Mitchell, 2010), but changing oceanic conditions with reduced oxygen contents of shallow waters led first to the demise of carbonate platforms together with their caprinuloideids towards the end of the Albian and then the deposition of organic rich shales (La Luna Formation and equivalents) in Venezuela, Trinidad and Colombia from the Cenomanian to the Campanian (Lo Mónaco et al., 2002).
Only in Mexico (e.g., Guerrero-Morelos Platform) did carbonate platforms persist into the Cenomanian (Hernández-Romanoa et al., 1997; Aguilera-Franco, 2003), but no caprinuloideids have so far been described from these platforms. The presence of Cobbanicaprina gen. nov. in Montana indicates that the Caprinuloideinae did not become extinct at the end of the Albian but persisted into the Cenomanian. Whether they inhabited carbonate platforms in Mexico and have yet to be described, or whether they found a
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Fig. 5. Cobbanicaprina bighornensis gen. nov. sp. nov. Holotype (USNM 547507). 1, transverse section, abumbonal view, showing myocardinal features. 2, transverse cross section, upper end of specimen, adumbonal view, note ligament. 3, natural section showing tabulae in body cavity. 4, flank showing weathered pallial canals. Symbols: r, ridge; pt, posterior tooth; at, anterior tooth; pm, posterior myophore; am, anterior myophore; bc, body cavity; t, tabulae. Scale bar ¼ 20 mm.
refuge in the Pacific is not known. However, the group clearly persisted into the Cenomanian and may have finally become extinct at OAE2. The occurrence of a caprinuloideid as far north as Montana in the Western Interior Seaway is also somewhat unexpected, but at least one other possible record exists from the Western Interior Seaway. Norman Sohl (written communication 1970, reported in Cobban et al. 1991) recorded a fragment of a rudist that had “affinities to the genus Tchthyosarcolithes” from a sandstone concretion in the Paguate Tongue of the Dakota Sandstone in northwestern New Mexico (USGS Mesozoic locality D7333 in the centre of sec. 5, T. 14 N., R. 12 W., McKinley County). This specimen came from the A. amphibolum ammonite Zone of the middle Cenomanian, that is at about the same level as the specimen from Montana. The specimen described in this paper from Montana was
collected from the base of the Soap Creek Bentonite which in recent sequence stratigraphic models for the Frontier Formation is placed at a transgressive surface of erosion (TSE) at the base of the Alkali Allomember between two (Peay and Torchlight allomembers) lowstand delta wedges (Hutsky, 2011, fig. 16). It seems unlikely that a rudist bivalve would live in such a deltaic setting and it is more likely that this is the final settling point of a floating shell that had dried out on a beach somewhere much further two the south and been carried into the Western Interior Seaway by surface currents. This would suggest that circulation patterns in the Western Interior Seaway saw warm surface tropical waters penetrating as far north as Montana which is consistent with circulation models suggesting an anticlockwise gyre operating in the Western Interior Seaway (e.g., Slingerland et al., 1996; Slingerman and Keen, 1999).
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Acknowledgements I thank Mark Florence and Kathy Hollis for facilitating my visit to the Smithsonian in September of 2012. I am indebted to Dra. Ma del Carmenn Perrilliat and Violeta Romero Mayen for allowing my access to the type collections of the Museum of Paleontology, Institute of Geology, Universidad Nacional Autónoma de México, Ciudad Uiversitaria, México. I thank the two anonymous reviewers for the comments that helped improve the paper. References Aguilar Pérez, J., 2008. Rudistas del cretácico inferior y medio. barremanocenomaniano, noreste, ventro y oeste de méxico. Tesis. Ciencias de la Tierra y del Espacio, 139 pp. Aguilera-Franco, N., 2003. Cenomanian e Coniacian zonation (foraminifers and calcareous algae) in the Guerrero e Morelos basin, southern Mexico. Revista Mexicana de Ciencias Geológicas 20, 202e222. Anderson, F.M., 1958. Upper Cretaceous of the Pacific Coast. Geological Society of America, Memoir 71, 378 pp. Bhattacharya, J.P., Willis, B.J., 2001. Lowstand deltas in the Frontier Formation, Powder River basin, Wyoming: implications for sequence stratigraphic models. AAPG Bulletin 85, 261e294. Brown, I., Mitchell, S.F., 2010. Lithostratigraphy of the Cretaceous succession in the Benbow Inlier, Jamaica. Caribbean Journal of Earth Science 41, 25e37. Carter, J.G., Altaba, C.R., Anderson, L.C., Araujo, R., Biakov, A.S., Bogan, A.E., Campbell, D.C., Campbell, M., Jin-hua, C., Cope, J.C.W., Delvene, G., Dijkstra, H.H., Zong-jie, F., Gavrilova, V.A., Goncharova, I., Guzhov, A.V., Harries, P.J., Hartman, J.H., Hautmann, M., Hoeh, W.R., Hylleberg, J., Bao-yu, J., Johnston, P., Kirkendale, L., Kleemann, K., Koppka, J., Krí z, J., Machado, D., Malchus, N., Márquez-Aliaga, A., Masse, J.-P., Middelfart, P.U., Mitchell, S., Nevesskaja, L.A., Özer, S., Pojeta Jr., J., Polubotko, I.V., Pons, J.M., Popov, S., Sánchez, T., Sartori, A.F., Scott, R.W., Sey, I.I., Jin-geng, S., Signorelli, J.H., Silantiev, V.V., Skelton, P.W., Steuber, T., Waterhouse, J.B., Wingard, G.L., Yancey, T., 2011. A Synoptical Classification of the Bivalvia (Mollusca). Paleontological Contributions number 4, 48 pp. University of Kansas. Cobban, W.A., 1987. Some Middle Cenomanian (Upper Cretaceous) acanthoceratid ammonites from the Western Interior of the United States. USGS Professional Paper 1445, 1-28, 13 pls. Cobban, W.A., Skelton, P.W., Kennedy, W.J., 1991. Occurrence of the rudistid Durania cornupastoris (des Moulins, 1826) in the Upper Cretaceous Greenhorn Limestone in Colorado. U.S. Geological Survey Bulletin 1985-D, D1eD8. Clark, C.K., 2010. Stratigraphy, Sedimentology, and Ichnology of the Upper Cretaceous Frontier Formation in the Alkali Anticline Region, Bighorn County, Wyoming. Unpublished thesis. University of Nebraska at Lincoln, Dissertations & Theses in Earth and Atmospheric Sciences. Paper 9. http://digitalcommons. unl.edu/geoscidiss/9. Damestoy, G., 1971. Essai de classification phylogénique des caprinidés (Lamellibranches). Bulletin du Muséum National d’Histoire Naturelle, Série 2 42, 1003e 1008. Gale, A.S., Voigt, S., Sageman, B.B., Kennedy, W.J., 2008. Eustatic sea-level record for the Cenomanian (Late Cretaceous) e extension to the Western Interior Basin, USA. Geology 36, 859e862. Hernández-Romanoa, U., Aguilera-Francob, N., Martın Martınez-Medranoa, M., Jaime Barceló-Duartea, J., 1997. Guerrero-Morelos Platform drowning at the CenomanianeTuronian boundary, Huitziltepec area, Guerrero State, southern Mexico. Cretaceous Research 18, 661e686. Hook, S.C., Cobban, W.A., 2013. Middle Turonian (Late Cretaceous) rudistids from the lower tongue of the Mancos Shale, Lincoln County, New Mexico. New Meixco Geology 35 (1), 13e20. February 2013. Hurd, T.J., 2012. Ichnology, Sedimentology, and Regional Sandstone Body Correlations of the Peay Member (Frontier Formation), Northeast Bighorn Basin, Wyoming, U.S.A. Unpublished thesis, University of Nebraska at Lincoln, Dissertations & Theses in Earth and Atmospheric Sciences. Paper 27. http:// digitalcommons.unl.edu/geoscidiss/27. Hutsky, A.J., 2011. Stratigraphic Analysis and Regional Correlation of Isolated, TopTruncated Shallow Marine Sandstone Bodies within the Upper Cretaceous Frontier Formation, Bighorn and Washakie Counties, Wyoming. Unpublished thesis, University of Nebraska at Lincoln, Dissertations & Theses in Earth and Atmospheric Sciences. Paper 17. http://digitalcommons.unl.edu/geoscidiss/17. Iba, Y., Sano, S., Skelton, P.W., Kagi, H., Tanabe, K., 2009. First record of Late Albian canaliculate rudist from northern California and re-assessment of Durania? californica Anderson, 1958. Cretaceous Research 30, 540e546. Kauffman, E.G., Johnson, C.C., 1988. The morphology and ecological evolution of middle and upper Cretaceous reef-building rudistids. Palaios 3, 194e216. Knechtel, M.M., Patterson, S.H., 1952. Bentonite deposits of the Yellowtail district, Montana and Wyoming. USGS Circular 150, 7. ́
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(Eds.), Revista mexicana de Ciencias geológicas. Number devoted to the Third international Conference on Rudists, 12 (2) (for 1995), 272-291, 4 figs., 3 pls., 2 tabs., Mexico City. Sano, S., Iba, Y., Skelton, P.W., Aguilar-Pérez, J., Tanabe, K., 2013. First record of Immanitas (Bivalvia, Hippuritida) from northern California, U.S.A. Caribbean Journal of Earth Science 45, 77e84. Schlanger, S.O., Jenkyns, H.C., 1976. Cretaceous anoxic events: causes and consequences. Geologie en Mijnbouw 55, 179e184. Schumacher, B.A., 2013. Bombers and Bivalves: First North American Occurrence of the Rudist Durania sp. (Bivalvia: Radiolitidae) in the Upper Cretaceous (Cenomanian) Greenhorn Limestone of Southeastern Colorado. Transactions of the Kansas Academy of Science 115 (3 & 4), 117e124. Scott, R.W., 1981. Biotic relations in early Cretaceous coral-algal-rudist reefs, Arizona. Journal of Paleontology 55, 463e478. Scott, R.W., 1990. Models and stratigraphy of mid-Cretaceous reef communities, Gulf of Mexico. SEPM (Society for Sedimentary Geology). Concepts in Sedimentology and Paleontology 2, 1e102. Scott, R.W., 2002. Albian caprinid rudists from Texas re-evaluated. Journal of Paleontology 76, 408e423. Scott, R.W., Hinote, R.E., 2007. Barremian-Early Aptian rudists, Sligo Formation, Texas, USA. In: Scott, R.W. (Ed.), Cretaceous rudists and carbonate platforms: environmental feedback. SEPM Special Publication No. 87, 237e246, Tulsa, Oklahoma. Skelton, P.W., 2013. Rudist classification for the revised Bivalvia volumes of the ‘Treatise on Invertebrate Paleontology. Caribbean Journal of Earth Science 45, 9e33. Skelton, P.W., Masse, J.-P., 1998. Revision of the Lower Cretaceous rudist genera Pachytraga Paquier and Retha Cox (Bivalvia: Hippuritacea) and the origins of the Caprinidae. In: Masse, J.-P., Skelton, P.W., (Coordinators) (Eds.), Quatrième Congrès International sur les Rudistes, Geobios e Mémoire spécial No. 22, pp. 331e370. Slingerland, R., Kump, L.R., Arthur, M.A., Fawcett, P.J., Sageman, B.B., Barron, E.J., 1996. Estuarine circulation in the Turonian Western Interior seaway of North America. GSA Bulletin 108, 941e952. Slingerman, R., Keen, T.R., 1999. Sediment transport in the Western Interior seaway of North America: predictions from a climate-ocean-sediment model. Isolated Shallow Marine Sand Bodies: Sequence Stratigraphic Analysis and Sedimentologic Interpretation. SEPM Special Publication No. 64, pp. 179e190. Steuber, T., 2002. Plate tectonic control on the evolution of Cretaceous platformcarbonate production. Geology 30, 259e262. Steuber, T., Löser, H., 2000. Species richness and abundance patterns of Tethyan Cretaceous rudist bivalves (Mollusca: Hippuritacea) in the central-eastern Mediterranean and Middle East. Palaeogeography, Palaeoclimatology, Palaeoecology 162, 75e104. Wyld, S.J., Umhoefer, P.J., Wright, J.E., 2006. Reconstructing northern Cordilleran terranes along known Cretaceous and Cenozoic strike-slip faults: Implications for the Baja British Columbia hypothesis and other models. In: Haggart, J.W., Enkin, R.J., Monger, J.W.H. (Eds.), Paleogeography of the North American Cordillera: Evidence For and Against Large-Scale Displacements, Geological Association of Canada, Special Paper 46, pp. 277e298.
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First record of a middle Cenomanian caprinuloideid rudist (Hippuritida, Bivalvia) from Montana, USA, and its geographical and stratigraphical significance Simon F. Mitchell Department of Geography and Geology, The University of the West Indies, Mona, Kingston 7, Jamaica
a r t i c l e i n f o
a b s t r a c t
Article history: Received 5 June 2013 Accepted in revised form 3 September 2013 Available online 23 October 2013
The new caprinoidean rudist bivalve Cobbanicaprina bighornensis gen. nov., sp. nov. is described from the upper middle Cenomanian of Big Horn County, Montana, USA. Cobbanicaprina gen. nov. is closely related to Mexicaprina and differs from that form in the absence of an external ligamental groove. The presence of Cobbanicaprina gen. nov. in the middle Cenomanian indicates that the Caprinuloideidae did not become extinct at the top of the Albian and persisted into the Cenomanian. The presence of this specimen so far north in the Western Interior Seaway is attributed to a dried-out individual specimen having been transported post-mortem by currents. Ó 2013 Elsevier Ltd. All rights reserved.
Keywords: Caprinoidea Caprinuloideidae Cenomanian Rudist bivalve Montana
1. Introduction The caprinoids (rudist bivalves) dominated the carbonate platforms of the mid Cretaceous but show contrasting patterns of development in the Old World and New World. In the Old World, the Caprinidae appeared in the Hauterivian and evolved to a peak of diversity in the early Aptian (Kauffman and Johnson, 1988; Skelton and Masse, 1998; Steuber and Löser, 2000). Following a mid Aptian extinction associated with Oceanic Anoxic Event 1a (OAE1a: Selli event), diversity remained low during the Albian, with a second peak in diversity during the Cenomanian before the group became extinct at OAE2 (Bonarelli event) in the late Cenomanian (Kauffman and Johnson, 1988; Philip and Airaud-Crumiere, 1991; Steuber and Löser, 2000). In contrast, the Caprinuloideidae of the New Word, which also appeared in the Hauterivian and saw a mid-early Aptian diversity peak and a mid Aptian extinction, reached their peak of diversity during the Albian and disappeared near the top of that stage, possibly at OAE1d (Breistroffer event) (Kauffman and Johnson, 1988; Skelton and Masse, 1998; Steuber, 2002; Scott, 2002; Scott and Hinote, 2007; Mitchell, 2013). Rudist bivalves characterized carbonate platform margins with less diverse assemblages in platform interior facies (Scott, 1990) and were particularly susceptible to Oceanic Anoxic Events (Schlanger and Jenkyns, 1976), when oxygen depleted waters E-mail address: [email protected]. 0195-6671/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cretres.2013.09.001
invaded the platforms and poisoned the biota leading to mass extinctions. Rudist bivalves are also occasionally found away from platform limestone facies in diverse sedimentary rock types ranging from chalks to mudstones to sandstones. In many cases their highly porous shells, which were filled with cells or pallial canals, may have enabled specimens that had dried out on beaches to float considerably distances (just as pumice can) and eventually when their shells became waterlogged they would sink to the sea floor. Away from the carbonate platforms of the AptianeAlbian of Texas and Arizona (Scott, 1981; Scott, 1990), rudist bivalves are rare in North American deposits (Anderson, 1958; Cobban et al., 1991; Hook and Cobban, 2013; Schumacher, 2013) and rather than specimens growing in situ might be the result of such floating specimens. Amongst these occurrences, specimens containing pallial canals have often been referred to Tchthyosarcolithes or Tchthyosarcolithes corelloidea (Hall and Meek). The revision of some of these records, as well as new records, indicates some of these specimens recorded from the Albian belong to the Caprinuloideidae (Iba et al., 2009; Sano et al., 2013). To date, however, no undoubted caprinuloideids have been recorded from undoubted post-Albian strata. During a visit to the Smithsonian in 2012, I discovered in the collections a well-preserved specimen of a pallial-canal bearing rudist from the upper middle Cenomanian of Montana (Fig. 1). This specimen has very good documentation and forms the basis of the current paper.
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Fig. 1. Map of North America showing the Western Interior Seaway extending from Texas to Canada and the location of reported specimens of Cenomanian (solid circles) and Turonian (open circles) rudists (data from Cobban et al., 1991; Hook and Cobban, 2013; Schumacher, 2013). Collection location of Cobbanicaprina bighornensis gen. nov., sp. nov. is the large black circle in Montana. Abbreviations for US states: MT, Montana; ND, North Dakota; SD, South Dakota; CO, Colorado; NE, Nebraska; AZ, Arizona; NM, New Mexico; TX, Texas; OK, Oklahoma. Land areas (Laramidia and Appalachia) shaded.
2. Provenance of specimen The specimen (USNM 547507) was collected from USGS Locality number 22869, and has the details of the specimen written on what is clearly an old piece of paper with the specimen that reads “Tchthyosarcolithes corelloidea {sic} from base of Soap Creek Bentonite at the top of Frontier Formation, Loc. NW ¼, SW ¼ Sec 31, T 7 S, R 32 E, Big Horn County, Mont.” (Fig. 2), which is in the Hardin District, and the specimen is listed as having been collected by “S.H. Patterson Sept. 1947” (Fig. 2). The specimen was presumably collected during Knechtel and Patterson’s study of the bentonites of Montana and Wyoming (Knechtel and Patterson, 1952, 1955, 1956, 1962). Sam H. Patterson joined the study in 1947 and measured and sampled the bentonite beds in the late summer and autumn of 1947 (Knechtel and Patterson, 1956, p. 1, 4) which is consistent with the collection date on the label (Fig. 2). Silicification of the specimen is
Fig. 2. Specimen label for Cobbanicaprina bighornensis gen. nov., sp. nov. preserved with the specimen in the Smithsonian.
also consistent with silicification associated with bentonites in Montana (Knechtel and Patterson, 1956, p. 40) as well as with some silicified specimens of the ammonite Cunningtoniceras amphibolum fallense Cobban lying on top of the Soap Creek Bentonite (Cobban, 1987, p. 15). Additionally, the Soap Creek Bentonite is referred to as lying on top of the Frontier Formation, which would have been consistent with earlier literature (e.g., Richards and Rogers, 1951), but which was changed by Knechtel and Patterson (1956) who placed the Soap Creek Bentonite in the Hardin district in the upper part of the Belle Fourche Member of the Cody Shale. The consistency of the information on a clearly old, and probably original label, identifying the specimen as a Tchthyosarcolithes (a canal bearing rudist) and the correct links to the time when Sam H. Patterson was doing fieldwork, demonstrate that the origin and the age of the specimen can be relied upon. The matrix in the body cavity has, however, been silicified preventing a direct comparison with the sediments of the Frontier Formation or Belle Fourche Member or checking for nannofossils. The locality NW ¼, SW ¼ Sec 31, T 7 S, R 32 E from which the rudist was collected is situated in the Big Horn Mountains to the south of the Soap Creek oil field within the drainage area of Soap Creek, about 20 miles (32 km) south of St. Xavier (Knechtel and Patterson, 1956, p. 86). In this area the Soap Creek bentonite is extensively exposed and averages 16 feet (5 m) in thickness. The Soap Creek Bentonite (also called the F Bed, X bentonite or Greyered bentonite), dated using 40Ar/39Ar at 94.93 .53 Ma (Obradovich, 1993; Fig. 3), is a thick regional marker in the Acanthoceras amphibolum ammonite zone. Richards and Rogers (1951) stated that the Soap Creek Bentonite was situated at the top of the siliciclastic deltaic sandstones of the Frontier Formation in Big Horn and Yellowstone Counties, Montana. In contrast, Knechtel and Patterson (1956) placed the Soap Creek Bentonite in the upper part of the Belle Fourche Member of the Cody Shales (but now regarded as member in the Frontier Formation) based on the presence of marine fossils and the dominance of shale lithologies in Big Horn County. The Frontier Formation represents a series of deltas on the western margin of the Western Interior Seaway produced either through progradation or forced regression (e.g.,
Fig. 3. Stratigraphy of Cenomanian in Montana and Wyoming with ammonite zones and dated bentonites (after Gale et al., 2008). Cobbanicaprina bighornensis gen. nov. sp. nov. was collected from the Soap Creek Bentonite.
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Bhattacharya and Willis, 2001; Clark, 2010; Hutsky, 2011; Hurd, 2012). 3. Systematic Palaeontology The classification used here follows Carter et al. (2011), Skelton (2013) and Mitchell (2013). Abbreviations used: RV, right valve; LV, left valve; ct, central tooth; at/ats, anterior tooth/socket; pt/pts, posterior tooth/socket; am, anterior myophore; pm, posterior myophore. Order Hippuritida Newell, 1965 Suborder Radiolitidina Skelton, 2013 Superfamily Caprinoidea d’Orbigny, 1847 Family Caprinuloideidae Damestoy, 1971 Subfamily Caprinuloideinae Damestoy, 1971 Genus Cobbanicaprina gen. nov. Type species. Cobbanicaprina bighornensis gen. nov. sp. nov. Derivation of name. After William A. Cobban for his work on the Cretaceous deposits of North America. Diagnosis. A genus of Caprinuloideinae with an elongate cylindrical RV. There is no external ligamental groove. The socket for the at is large and bifid and that for the pt is small. The am is attached to a surface (ledge) on the anterior side of the shell; the pm fitted into an elongate socket on the posterior side of the at socket. The ct is ‘knee’-shaped. The shell wall and ct are filled with rounded to polygonal pallial canals. Distribution. Only known from the upper middle Cenomanian of Big Bend County, Montana. Discussion. Although only a single specimen is available, the specimen shows distinctive diagnostic characters that not only allows it to be described but allows its relationship with the subfamily Caprinuloideinae to be evaluated in detail. As such the erection of a new genus based on a single RV is considered warranted. Cobbanicaprina gen. nov. shows characters in common with many Albian caprinuloideids but also has differences (Fig. 4). Like Neokimbleia Mitchell and Youngicaprina Mitchell, Cobbanicaprina gen. nov. lacks an external ligamental groove. In Caprinuloidea Palmer and Youngicaprina the ct is straight and extends down to the body cavity (Fig. 4.5e4.6); in Mexicaprina Coogan and Cobbanicaprina the ct is knee-shaped extending first towards the posterior side of the shell and then bending towards the ventral margin of the shell (Fig. 4.1e4.2); in Kimbleia Coogan and Neokimbleia the ct is thickened dorso-ventrally, extends a short way towards the posterior side of the shell and then extends towards the ventral margin as a narrow septum (Fig. 4.2e4.3). The form of the pm in Cobbanicaprina (judging from the form of the cavity it fitted into in the RV) is similar to that of Mexicaprina, Kimbleia and Neokimbleia and did not extend along the posterior side of the body cavity (Fig. 4.1e 4.4). Youngicaprina is further differentiated by the form of its myophores, particularly the bladed am. Some specimens of Mexicaprina also have a bifid tooth which is also seen in Immanitas Palmer (Aguilar Pérez, 2008). Cobbanicaprina gen. nov. can therefore be seen as an evolutionary development from Mexicaprina that developed by the loss of an external ligamental groove. This is comparable to the loss of the external ligamental grooves in the evolution of Neokimbleia from Kimbleia and of Youngicaprina from Texicaprina Coogan (Mitchell, 2013). Cobbanicaprina gen. nov. differs from Tchthyosarcolithes in the form of its pm. In Tchthyosarcolithes the pm attaches directly to the body cavity, whereas in Cobbanicaprina gen. nov. it fits into an accessory cavity separated from the body cavity by a septum. Equally, Cobbanicaprina is distinguished from Old World
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Cenomanian caprinids such as Caprina by its myocardinal arrangement with the pm being rotated downwards and outwards from the LV to face outwards onto the accessory cavity wall in the RV (the converse is true in Caprina and other caprinids). Cobbanicaprina bighornensis gen. nov. sp. nov. Figs. 4.1, 5 Derivation of name. After Big Horn County, Montana, where the specimen was collected. Holotype. Smithsonian Institute, No. USNM 547507, from the base of the Soap Creek Bentonite (upper middle Cenomanian), Big Horn County, Montana. Diagnosis. Same as genus. Description. The holotype is an incomplete RV with a preserved length of 169 mm and a maximum diameter of 57 mm. The specimen has been silicified preserving full details of the shell construction. Parts of the exterior have been weathered away to show the pallial canals comprising the outer layer of the inner shell material, but around part of the exterior the very thin outer layer is preserved. The body cavity is rounded pentagonal in form (Fig. 5.1), and has a maximum diameter of 22 mm which is about 37% of the estimated original diameter of the shell at that point. The body cavity is filled with spaced concave to commissure tabulae (Fig. 5.3). The myocardinal features can be seen in a natural transverse cross section (Fig. 5.1) as well as on the upper weathered surface of the specimen (Fig. 5.2). This upper weathered surface has tabulae in the body cavity and is at a level somewhere below the commissure of the original shell. The socket for the at tooth is large and bifid, with a wedge of pallial canal-bearing shell material forming a triangular ridge on the antero dorsal side (Fig. 5.1). The socket for the pt is much smaller than that of the at, and is pear-shaped. On its dorsal side, the socket for the pt is partially penetrated by a short, narrow ridge (Fig. 5.1). There is no external ligamental groove. The socket/attachment for the am is seen as a surface within the pallial canal-bearing shell structure on the anterior side of the shell; this surface begins near the triangular ridge which projects into the at socket, and runs along the anterior side of the body cavity about midway through the shell structure. The socket for the pm is a dorso-ventrally elongated cavity on the posterior side of the at socket, and is filled with four larger polygonal pallial canals and several triangular smaller ones (Fig. 5.1). The ct is ‘knee’-shaped, the part between the sockets for the pt and at being filled with small pallial canals and the portion between the socket for the am and cavity for the pm being filled with elongated pallial canals. The pallial canals in the outermost part of the shell structure, where they are preserved, range from slightly to strongly elongated; some are weakly pyriform with their outer ends being a little narrower than their inner ends. The remainder of the shell structure is filled with rounded to polygonal pallial canals, which contain concave tabulae. 4. Discussion The discovery of a Cenomanian caprinuloideinid requires a review of the evolutionary development of the Caprinuloideidae. While caprinuloideids were widespread in the Aptian and Albian of the New World, the end of the Albian saw a major demise of carbonate platforms across the region (Kauffman and Johnson, 1988; Steuber and Löser, 2000). In North America uplift of the American Cordillera (Wyld et al., 2006) saw the influx of fine grained clastics in the latest Albian to Cenomanian caused the collapse of carbonate platforms of Arizona and Texas and the disappearance of the caprinuloideids. Further south in the Caribbean province, carbonate
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Fig. 4. Comparison of the RV of Cobbanicaprina gen.nov. with RVs of selected Albian caprinuloideids. All specimens shown in transverse section adumbonal view (cross sections where appropriate, flipped horizontally, so all specimens are viewed in same orientation) with the body cavity placed at the bottom. 1. Cobbanicaprina bighornensis gen nov. sp. nov., transverse cross section, original abumbonal view (here flipped horizontally), showing myocardinal features (USNM 547507); 2, Mexicaprina quadrata Alencáster and Oviedo-García, RV (IGM.4581), apertural face, late Albian of El Madroño, state of Querétaro, central Mexico; 3, Kimbleia albrittoni (Perkins 1960), RV (UT.203571), original abumbonal view (here flipped horizontally), transverse cross section, Segovia Formation, Lopez Ranch, Kimble County, Texas; 4, BeE, Neokimbleia planata (Conrad). RV (IGM.2575), original abumbonal view (here flipped horizontally), transverse cross section, El Abra Formation, Mexico; 5, Youngicaprina gloria Mitchell, RV (IGM.7643), apertural view showing myocardinal elements, late Albian of El Madroño, state of Querétaro, central Mexico; 6, Caprinuloidea romeri Mitchell, transverse section of RV, original abumbonal view (here flipped horizontally), showing teeth and myophores (SI.USNM.PAL.534223), Edwards Limestone, Whitney Dam, Texas. Abbreviations: l, ligament; ats, anterior tooth socket; ct, central tooth; pts, posterior tooth socket; am, anterior myophore; pm, posterior myophore; bc, body cavit. Scale bars, 20 mm.
platforms had been widespread in the Greater Antilles and northern South America (e.g., Rojas et al., 1996; Brown and Mitchell, 2010), but changing oceanic conditions with reduced oxygen contents of shallow waters led first to the demise of carbonate platforms together with their caprinuloideids towards the end of the Albian and then the deposition of organic rich shales (La Luna Formation and equivalents) in Venezuela, Trinidad and Colombia from the Cenomanian to the Campanian (Lo Mónaco et al., 2002).
Only in Mexico (e.g., Guerrero-Morelos Platform) did carbonate platforms persist into the Cenomanian (Hernández-Romanoa et al., 1997; Aguilera-Franco, 2003), but no caprinuloideids have so far been described from these platforms. The presence of Cobbanicaprina gen. nov. in Montana indicates that the Caprinuloideinae did not become extinct at the end of the Albian but persisted into the Cenomanian. Whether they inhabited carbonate platforms in Mexico and have yet to be described, or whether they found a
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Fig. 5. Cobbanicaprina bighornensis gen. nov. sp. nov. Holotype (USNM 547507). 1, transverse section, abumbonal view, showing myocardinal features. 2, transverse cross section, upper end of specimen, adumbonal view, note ligament. 3, natural section showing tabulae in body cavity. 4, flank showing weathered pallial canals. Symbols: r, ridge; pt, posterior tooth; at, anterior tooth; pm, posterior myophore; am, anterior myophore; bc, body cavity; t, tabulae. Scale bar ¼ 20 mm.
refuge in the Pacific is not known. However, the group clearly persisted into the Cenomanian and may have finally become extinct at OAE2. The occurrence of a caprinuloideid as far north as Montana in the Western Interior Seaway is also somewhat unexpected, but at least one other possible record exists from the Western Interior Seaway. Norman Sohl (written communication 1970, reported in Cobban et al. 1991) recorded a fragment of a rudist that had “affinities to the genus Tchthyosarcolithes” from a sandstone concretion in the Paguate Tongue of the Dakota Sandstone in northwestern New Mexico (USGS Mesozoic locality D7333 in the centre of sec. 5, T. 14 N., R. 12 W., McKinley County). This specimen came from the A. amphibolum ammonite Zone of the middle Cenomanian, that is at about the same level as the specimen from Montana. The specimen described in this paper from Montana was
collected from the base of the Soap Creek Bentonite which in recent sequence stratigraphic models for the Frontier Formation is placed at a transgressive surface of erosion (TSE) at the base of the Alkali Allomember between two (Peay and Torchlight allomembers) lowstand delta wedges (Hutsky, 2011, fig. 16). It seems unlikely that a rudist bivalve would live in such a deltaic setting and it is more likely that this is the final settling point of a floating shell that had dried out on a beach somewhere much further two the south and been carried into the Western Interior Seaway by surface currents. This would suggest that circulation patterns in the Western Interior Seaway saw warm surface tropical waters penetrating as far north as Montana which is consistent with circulation models suggesting an anticlockwise gyre operating in the Western Interior Seaway (e.g., Slingerland et al., 1996; Slingerman and Keen, 1999).
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Acknowledgements I thank Mark Florence and Kathy Hollis for facilitating my visit to the Smithsonian in September of 2012. I am indebted to Dra. Ma del Carmenn Perrilliat and Violeta Romero Mayen for allowing my access to the type collections of the Museum of Paleontology, Institute of Geology, Universidad Nacional Autónoma de México, Ciudad Uiversitaria, México. I thank the two anonymous reviewers for the comments that helped improve the paper. References Aguilar Pérez, J., 2008. Rudistas del cretácico inferior y medio. barremanocenomaniano, noreste, ventro y oeste de méxico. Tesis. Ciencias de la Tierra y del Espacio, 139 pp. Aguilera-Franco, N., 2003. Cenomanian e Coniacian zonation (foraminifers and calcareous algae) in the Guerrero e Morelos basin, southern Mexico. Revista Mexicana de Ciencias Geológicas 20, 202e222. Anderson, F.M., 1958. Upper Cretaceous of the Pacific Coast. Geological Society of America, Memoir 71, 378 pp. Bhattacharya, J.P., Willis, B.J., 2001. Lowstand deltas in the Frontier Formation, Powder River basin, Wyoming: implications for sequence stratigraphic models. AAPG Bulletin 85, 261e294. Brown, I., Mitchell, S.F., 2010. Lithostratigraphy of the Cretaceous succession in the Benbow Inlier, Jamaica. Caribbean Journal of Earth Science 41, 25e37. Carter, J.G., Altaba, C.R., Anderson, L.C., Araujo, R., Biakov, A.S., Bogan, A.E., Campbell, D.C., Campbell, M., Jin-hua, C., Cope, J.C.W., Delvene, G., Dijkstra, H.H., Zong-jie, F., Gavrilova, V.A., Goncharova, I., Guzhov, A.V., Harries, P.J., Hartman, J.H., Hautmann, M., Hoeh, W.R., Hylleberg, J., Bao-yu, J., Johnston, P., Kirkendale, L., Kleemann, K., Koppka, J., Krí z, J., Machado, D., Malchus, N., Márquez-Aliaga, A., Masse, J.-P., Middelfart, P.U., Mitchell, S., Nevesskaja, L.A., Özer, S., Pojeta Jr., J., Polubotko, I.V., Pons, J.M., Popov, S., Sánchez, T., Sartori, A.F., Scott, R.W., Sey, I.I., Jin-geng, S., Signorelli, J.H., Silantiev, V.V., Skelton, P.W., Steuber, T., Waterhouse, J.B., Wingard, G.L., Yancey, T., 2011. A Synoptical Classification of the Bivalvia (Mollusca). Paleontological Contributions number 4, 48 pp. University of Kansas. Cobban, W.A., 1987. Some Middle Cenomanian (Upper Cretaceous) acanthoceratid ammonites from the Western Interior of the United States. USGS Professional Paper 1445, 1-28, 13 pls. Cobban, W.A., Skelton, P.W., Kennedy, W.J., 1991. Occurrence of the rudistid Durania cornupastoris (des Moulins, 1826) in the Upper Cretaceous Greenhorn Limestone in Colorado. U.S. Geological Survey Bulletin 1985-D, D1eD8. Clark, C.K., 2010. Stratigraphy, Sedimentology, and Ichnology of the Upper Cretaceous Frontier Formation in the Alkali Anticline Region, Bighorn County, Wyoming. Unpublished thesis. University of Nebraska at Lincoln, Dissertations & Theses in Earth and Atmospheric Sciences. Paper 9. http://digitalcommons. unl.edu/geoscidiss/9. Damestoy, G., 1971. Essai de classification phylogénique des caprinidés (Lamellibranches). Bulletin du Muséum National d’Histoire Naturelle, Série 2 42, 1003e 1008. Gale, A.S., Voigt, S., Sageman, B.B., Kennedy, W.J., 2008. Eustatic sea-level record for the Cenomanian (Late Cretaceous) e extension to the Western Interior Basin, USA. Geology 36, 859e862. Hernández-Romanoa, U., Aguilera-Francob, N., Martın Martınez-Medranoa, M., Jaime Barceló-Duartea, J., 1997. Guerrero-Morelos Platform drowning at the CenomanianeTuronian boundary, Huitziltepec area, Guerrero State, southern Mexico. Cretaceous Research 18, 661e686. Hook, S.C., Cobban, W.A., 2013. Middle Turonian (Late Cretaceous) rudistids from the lower tongue of the Mancos Shale, Lincoln County, New Mexico. New Meixco Geology 35 (1), 13e20. February 2013. Hurd, T.J., 2012. Ichnology, Sedimentology, and Regional Sandstone Body Correlations of the Peay Member (Frontier Formation), Northeast Bighorn Basin, Wyoming, U.S.A. Unpublished thesis, University of Nebraska at Lincoln, Dissertations & Theses in Earth and Atmospheric Sciences. Paper 27. http:// digitalcommons.unl.edu/geoscidiss/27. Hutsky, A.J., 2011. Stratigraphic Analysis and Regional Correlation of Isolated, TopTruncated Shallow Marine Sandstone Bodies within the Upper Cretaceous Frontier Formation, Bighorn and Washakie Counties, Wyoming. Unpublished thesis, University of Nebraska at Lincoln, Dissertations & Theses in Earth and Atmospheric Sciences. Paper 17. http://digitalcommons.unl.edu/geoscidiss/17. Iba, Y., Sano, S., Skelton, P.W., Kagi, H., Tanabe, K., 2009. First record of Late Albian canaliculate rudist from northern California and re-assessment of Durania? californica Anderson, 1958. Cretaceous Research 30, 540e546. Kauffman, E.G., Johnson, C.C., 1988. The morphology and ecological evolution of middle and upper Cretaceous reef-building rudistids. Palaios 3, 194e216. Knechtel, M.M., Patterson, S.H., 1952. Bentonite deposits of the Yellowtail district, Montana and Wyoming. USGS Circular 150, 7. ́
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